We are currently investigating the immunopathogenesis of Pneumocystis carinii pneumonia, including both humoral and cellular factors in humans. The role of humoral factors is being investigated by experiments looking at levels of cytokine (TNF, IL6, IL8) protein and expression of cytokine genes in bronchoalveolar lavage fluid and cell pellets from patients with P. carinii pneumonia who have undergone serial bronchoscopies. The role of host cellular elements is being investigated by looking at the interaction of host cells (peripheral blood leukocytes, cultured alveolar epithelial cells, alveolar macrophage) with P. carinii and with a purified P. carinii antigen. Inflammatory cell function, surfactant production, and cytokine production in these cells will be measured.